GOOD GRAB: Derek Hagan is among several productive additions Giants GM Jerry Reese (inset) has made during the season. Photo: Anthony J. Causi/New York Post

GOOD GRAB: Derek Hagan is among several productive additions Giants GM Jerry Reese (above) has made during the season. (Paul J. Bereswill)

The top of the roster might be good enough to take the Giants deep into the playoffs.

But it is the bottom of the roster that will determine if the Giants put themselves in position to get that far.

Unless Eli Manning, Justin Tuck and the other marquee talent come up big in January, the Giants won’t be doing much after New Year’s. But if not for some lesser lights among the 53 players, some of whom were picked up off the scrap heap, the Giants wouldn’t have as much as a sniff of the postseason scent as they venture deeper into December.

With bitter memories of the way last year’s team ran out of players down the stretch, general manager Jerry Reese this season vehemently made sure to fortify the depth. He should be in the discussion for Executive of the Year — and not only for the splashy signings of Antrel Rolle, Deon Grant and Keith Bulluck, and the drafting of Jason Pierre-Paul. The Giants would be sunk without their in-season imports, and Reese, director of pro personnel Dave Gettleman and his department have hit on several small moves that add up to big things.

“A lot of kudos go to guys that come in in the middle of the season,” Tuck said. “The reason we are still in this race is because a lot of guys have been thrown into the fire and have really stepped up.”

Derek Hagan won’t be confused with Hakeem Nicks or Steve Smith, but he was unemployed when the Giants resigned him three weeks ago as a stopgap. Hagan caught seven passes for 65 yards against the Redskins.

The special teams were dismal early but have been better of late. Brian Jackson, a rookie defensive back best known while with the Jets for getting duct-taped onto the goal post on “Hard Knocks,” has brought a toughness and attitude to coverage. Devin Thomas, a bust as a Redskins second-round draft pick, was released this season by teams with a combined record of 6-18 (Redskins, Panthers), yet in his Giants debut on Sunday he made three impact plays on special teams.

Tight end Bear Pascoe began the season on the practice squad, was signed after the first game and was pretty much a spare part until Madison Hedgecock went down with a hamstring injury. Pascoe has served as the fullback the last eight games, learned a new position and been an asset.

Reese tried to solve the kick and punt return woes by trading for Darius Reynaud, a move that hasn’t paid off. And so, Reese got back at it and took a gamble on Will Blackmon, a Packers castoff coming off major knee surgery. Blackmon was a slight upgrade until he suffered a chest injury.

Heck, even Sage Rosenfels — acquired along with Reynaud from the Vikings as a response to Jim Sorgi’s shoulder injury — has made a difference even though he hasn’t thrown a single pass. Has anyone noticed that ever since Rosenfels eight games ago replaced rookie Matt Dodge as the holder, Lawrence Tynes is 13-for-13 on field goals?

“I guess you give Jerry Reese a lot of credit for going out and getting guys that can fit this system in a hurry-up mode,” Tuck said.

Ex-Eagle Shawn Andrews was and is a medical risk following back surgery, but he had the coaching staff fired up after his three fill-in starts at left tackle, buying time for others to heal before re-injuring his back.

As key players get healthier, the trickle-down means the depth should only improve, a good sign for the upcoming holiday season, when enough is rarely enough.

Favre sits out practice, streak in jeopardy

Brett Favre is not going to practice today as he deals with a sprained right shoulder, a new injury that could put an end to his streak of 297 consecutive starts as the Vikings get ready for Sunday’s game against the Giants.

“He probably won’t practice [today] but we’ll get a chance to see how he looks tomorrow and just try to make a determination based on that, you know, how things will look for Sunday,” interim Vikings coach Leslie Frazier said yesterday on Sirius XM’s Mad Dog Radio. “But we’re all hoping that he’ll be healthy enough to play.”

Although backup Tarvaris Jackson stepped in last Sunday and directed the Vikings to a 38-14 victory over the Bills — Favre was hurt on his first pass of the game — Frazier said immediately after that game that Favre is the starter as long as he’s healthy.

➤ A spokesman for former Jets game hostess Jenn Sterger, who allegedly received inappropriate phone messages and photos from Favre, says they are concerned that the quarterback will be retired before the NFL concludes its investigation.

Sterger manager Phil Reese says his client wants the investigation finished during the season because Favre has said he will retire at the end of this year, at which point he may no longer be susceptible to punishment from the league.

Yikes, it’s the Vikes

Is it the color purple? Is it that he gets confused which of the Twin Cities is which?

Whatever the reason, no team brings out the worst in Eli Manning like his next opponent, the Vikings.

Manning is 0-4 against them, but if you want to put an asterisk on the 2008 game, go ahead. The Giants had the No. 1 seed in the NFC locked up and Manning in the regular-season finale played only the first half of an eventual 20-19 loss.

Manning usually plays well in domes, but he’s 0-2 at Mall of America Field. In the four losses, Manning has thrown two touchdown passes and nine interceptions.

Manning always low-keys personal duels, and you can be sure he will do the same this week. You can also be sure he’s sick and tired of getting beat by the Vikings.